Research Journal of Applied Sciences, Engineering and Technology 5(7): 2332-2339, 2013
ISSN: 2040-7459; e-ISSN: 2040-7467
© Maxwell Scientific Organization, 2013
Submitted: June 13, 2012
Accepted: August 28, 2012
Published: March 11, 2013
Gas Chromatography/Electron Ionization Mass Spectrometric Analysis of Oligomeric
Polyethylene Glycol Mono Alkyl Ethers
1
1
Adebayo O. Onigbinde, 2Burnaby Munson and 3Bamidele M.W. Amos-tautua
Department of Basic Sciences, Chemistry Unit, Babcock University, Ilishan, Remo, Ogun State, Nigeria
2
Department of Chemistry and Biochemistry, University of Delaware Newark DE, 19716, USA
3
Department of Chemistry, Niger-Delta University, Bayelsa State, Nigeria
Abstract: Polyethylene Glycol Monoalkyl Ethers, CxH2x+1 (OC2H4)n OH, (PEGMAE), are polar compounds like
Polyethylene Glycols (PEG) and they undergo microbial degradation which produces toxic substances that are
potentially dangerous to the environment. Therefore, the purpose of this study is to carry out proper identification
and characterization of these compounds. The Electron Ionization (EI) and Chemical Ionization (CI) spectra of
various PEGMAE were obtained by Gas Chromatography/Mass Spectrometry (GC/MS) and were used to identify
and characterize these compounds. The characteristic cleavages in the EI and CI reactions of PEGMAEs were also
studied. The results obtained showed that the methane CI mass spectra of the PEGMAE contain MH+ ions and
fragment ions similar to those found in their EI mass spectra. The relative abundances of the MH+ ions are low,
variable and increase with increasing sample size across the chromatographic peaks; but do not increase with
increasing x or n. The base peaks of the low mass oligomers (x3) are PEG related (e.g., m/z 45, 59) but those of
higher mass oligomers (x4) include the ion at m/z 63 (HOC2H4OH) H+ or m/z 107 (HO (C2H4O)2 H) H+. There are
no (MH-H2O)+ ions or protonated dimer ions (n2, x2) in the spectra of PEGMAE. The Relative Molar
Sensitivities (RMS) or the Relative Sensitivity per Gram (RSG) increases linearly with molecular polarizabilty or
molecular weight with a non-zero intercept.
Keywords: Electron, methane chemical ionization, polyethylene glycol ethers
INTRODUCTION
Polyethylene Glycol Monoalkyl Ethers, CxH2x+1
(OC2H4)n OH (PEGMAE), are polar compounds like
Polyethylene Glycols (PEG) and are extensively used
for many industrial purposes: in cleaning formulations,
detergents, agriculture (Coble and Brumbaugh, 1993;
Steber and Wierich, 1985) pharmaceuticals, alkaline
batteries, tin electroplating, lubricants, coating agents
and in textile fibres (Forkner et al., 1994; Aronstein
et al., 1991). However, the widest application of
PEGMAE is in the field of surfactants where they are
used in formulating PEG based anionic, cationic or non
ionic surfactants (Evans et al., 1994). Because of the
large production of PEGMAE, some oligomers have
been found in environmental samples but are
considered less environmentally harmful than ionic
surfactants, but they still undergo microbial degradation
that produces toxic substances that are potentially
dangerous to the environment. Ethylene glycol and its
oligomers are readily biodegradable and are not
considered as persistent in the environment (Forkner
et al., 1994) but ethylene glycol derivatives have been
observed in environmental samples (Sheldon and Hites,
1979). Evidence has been presented that ethylene glycol
and ethylene glycol alkyl monomers have tetratogenic
effects (Nadeau, 1964) if consumed in high doses. The
metabolites of PEG ethers are usually aldehydes and
carboxylic acids which are responsible for their toxic
effects in animals (Nadeau, 1964). The wide usage of
and inappropriate disposal of containers of polyethylene
glycols and the corresponding ethers makes them
inevitable pollutants. Despite the attempts to degrade
industrial effluents, some still find their way into rivers,
water, wells and the soil, suggesting that some of them
are bioresistant (Cox, 1978; Kloster et al., 1993;
Watson and Jones, 1977). Allgood et al. (1990)
reported that separation of higher molecular weight
oligomers of PEGMAE (x6, n5) by Gas
Chromatography (GC) and Mass Spectrometry (MS)
are difficult because of their low volatility. Puthoff and
Benedict (1961), separated some phenyl-azo derivatives
of PEGMAE’s (n = 1 - 2) oligomers and report of GC
separation of nonylphenol ethoxylates was also made in
earlier studies (Anghel et al., 1994; Favretto et al.,
1978; Stephanou and Giger, 1982). The Electron
Ionization (EI) spectra of low mass PEGMAE, like
those of similar hydrocarbons, alcohols and ethers,
Corresponding Author: Adebayo O. Onigbinde, Department of Basic Sciences, Chemistry Unit, Babcock University, Ilishan,
Remo, Ogun State, Nigeria
2332
Res. J. Appl. Sci. Eng. Technol., 5(7): 2332-2339, 2013
show low abundance of molecular ions (x≤3, n = 1-4)
while the higher members of this series (x≥4 for al n)
do not contain molecular ions. Most of the mass spectra
of PEGMAE available in the literature are spectra of
phenyl, methyl, trimethylsilyl derivatives (Cross, 1987;
Stein, 1997) including the EI mass spectra of mixtures
of C12-C14 ethoxylated alcohols, with up to twenty units
of ethylene oxide, obtained by direct insertion into the
source of the mass spectrometer (Julia-Danes and
Casanovas, 1979). Because of the low volatility of these
compounds, other techniques such as potentiometer,
High Pressure Liquid Chromatography (HPLC), Thin
Layer Chromatography (TLC) etc., have been used to
analyze mixtures of PEGMAE (Cross, 1987). Proper
identification of these compounds is impossible except
other methods such as Chemical Ionization (CI) are
used to obtain molecular weight information.
PEGMAE have a hydrophobic group and a
hydrophilic group with an ether group sandwiched
between them. The focal point of removing an electron
from these compounds is either from the internal
oxygen (ether) or the terminal (hydroxyl) oxygen. Other
results given by McLafferty and Turecek (1993) and
Williams and Howe (1972) have shown that the EI
mass spectrum of PEGMAE include fragments
produced by the general fragmentation pattern of the
three classes of compounds such as: σ-cleavages
(CxH2x+1+, CxH2x-1+, CxH2x+), hydrogen rearrangements
(hydrocarbons, alcohols, ethers), inductive or chargesite cleavages (alcohols and ethers, CxH2x+1O+, CxH2x+
+
1O , CxH2xO ) and α-cleavages (alcohols, ethers, RCH2
+
= OH ).
Few EI mass spectra of PEGMAE are available in
the literature. In this present study, the EI and methane
chemical ionization (CH4 CI) mass spectra of several
PEGMAE will be obtained for proper identification and
characterization and a comparison with the few EI
spectra found in the NIST spectral data (Stein, 1997)
base will be made with those obtained in our laboratory.
Attempt will also be made to identify characteristic
cleavages that occur with EI and CI of PEGMAE’s.
MATERIALS AND METHODS
EI mass spectra of the PEGMAE were obtained by
GC/MS using Hewlett Packard (HP) 5970 Mass
Selective Detector (MSD) attached to an HP5980 gas
chromatograph, an HP 5972 MSD attached to an HP
5980A gas chromatograph and a Micro Mass/VG Auto
specQ mass spectrometer attached to an HP 5980 Series
II gas chromatograph. Each MSD was calibrated using
the automatic tuning procedure (Auto tune) with
peflurotributylamine, PFTBA as the standard.
Peflurokerosene, PFK was used to calibrate the Auto
SpecQ mass spectrometer.
Source temperatures of the MSD were ~250oC and
the transfer lines were ~280oC. A source temperature of
~200oC was used with the Auto SpecQ mass
spectrometer and Helium was used as the carrier gas at
a flow rate of 1 mL/min. EI ionization was done with
nominal electron energy of 70 eV. Separation of
mixtures of known concentrations of the lower
oligomers (n = 1-6) were achieved with 30×0.25 mm
cross-linked methyl silicone capillary columns (Alltech
SE-30, SE54) using temperature programs of ~35250°C at 5°C/min. Split less injections of 0.05-0.5 μL
sample were used for these experiments.
The reported EI and CI mass spectra are averages
of 3-5 spectra across the tops of the chromatographic
peaks, with background subtraction. The Total Ion
Current (TIC), was obtained by summing the ion
currents of all the sample ions over the mass range, 10500 μ. Solvent delay times (0.5-2.2 sec) were applied
for the analyses of some mixtures, but most of the
experiments were done with no solvent delay times.
Chemical Ionization (CI) mass spectra were obtained
using a VG MM-16 and the VG Auto SpecQ mass
spectrometers. Source pressures was measured as ~0.3
torr with a capacitance manometer (MKS Instruments,
Burlington, MA), connected directly into the source of
the mass spectrometer by a glass tube through the inlet
for the direct insertion probe. The ratios of the major
ions in the methane reagent gas with the 2 instruments
used in this study are similar: m/z 29/17 = 1, 19/17 =
0.02, 41/17 = 0.03 and 43/17 = 0.02 with the VG MM16 and m/z 29/17 = 0.65, 19/17 = 0.02, 41/17 = 0.11
and 43/17 = 0.04 with the VG Auto Spec Q mass
spectrometer (little H3O+ in the source).
RESULTS AND DISCUSSION
GC/EIMS of ethylene glycol monoalkyl ethers: The
EI mass spectra of ethylene glycol monohexyl ether and
ethylene glycol monodactyl ether are shown in Fig. 1.
The fragmentation patterns are similar to those in
the mass spectra of Ethoxylated Fatty Amines (EFA)
obtained by field desorption mass spectrometry, FD
(Weber et al., 1982). The major ions for both classes of
compounds (PEGMAE and EFA) occur in the lower
mass region and consist of ions with nominal
composition: CxH2x+1+ (15, 29, 43,...), CxH2x-1+ (27, 41,
55,...), CxH2x+ (28, 42, 56,...), CxH2x+1O+ (31, 45, 59,...),
CxH2x-1O+ (29, 43, 57,...), CxH2x+2OH+ (19, 33, 47,
61,...), CxH2xO+ (30, 44, 58,...), (HO (C2H4O)n H) H+
(63, 107, 151,...). The EI mass spectra of low molecular
weight hydrocarbons, alcohols and ethers have been
shown to contain low abundant molecular ions
(McLafferty and Turecek, 1993) but those of the
corresponding high molecular weight homologs do not
2333 Res. J. Appl. Sci. Eng. Technol., 5(7): 2332-2339, 2013
43
50.00
100
95
Ethylene
glycol
monohexyl
ether MW = 146
90
85
80
75
95 127
70
65
60
55
50
45
40
35
63
30
25
56
20
75
15
10 29
5
0
20 40 60 80 100 120 140 160 180 200 220 240
45 D
100
95
90
Diethylene Glycol
85
MW = 106
80
75
70
65
60
55
50
45
40
35
75 F
30
25
20 F 31
15
89 D
10
5
0
20 40 60 80 100 120 140 160 180 200 220 240
(a)
(a)
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
50.00
41 Ethylene glycol monohexyl ether MW = 202
57
45
29
71 85
63
97
29
20
117
140
171
40 60 80 100 120 140 160 180 200 220 240
45 D
Diethylene Glycol monomethyl ether
MW = 120
59 E
31
F75
20
E
103
40 60 80 100 120 140 160 180 200 220 240
(b)
(b)
59 E
100
95
Diethylene Glycol dimethyl ether
90
85
80
MW = 134
75
70
65
60
55
50
45
40
35 F 45 D
30 31
25
20
15
D 103E
89
10
133 D
5
0
20 40 60 80 100 120 140 160 180 200 220 240
Fig. 1: 70 eV GC/EI mass spectra of (a) ethylene glycol
monohexyl ether (b) ethylene glycol monodactyl ether
on VG auto SpecQ
contain detectable molecular ions (Stein, 1997; Weber
et al., 1982). Similarly, the EI spectra of PEGMAE
(x≥4) consist mostly of low mass fragment ions and no
high mass fragment ions of significant abundance to
allow unambiguous determination of their molecular
weights. However, the (M+1)+ ions reported by Tanaka
and Igarashi (2004); in the EI mass spectra of a mixture
of ethoxylated fatty alcohols (C12-C14) must have
resulted from ion-molecule reactions.
For short alky chain PEGMAE, (x = 1-2), the EI
spectra are similar to the mass spectra of the analogous
PEG oligomers and their dimethyl ethers reported by
Favretto et al. (1978) (Fig. 2). The 70 eV EI mass
spectra of EGMAE, CxH2x+1OC2H4OH, obtained by two
instruments in our laboratory and the literature data
(Coble and Brumbaugh, 1993) for the lower oligomers
(x = 1-9), are similar to each other. However, there are
significant differences among the relative abundances
of the major ions in the spectra obtained in this
(c)
Fig. 2: GC/EI 70 eV mass spectra of (a) diethylene glycol, (b)
diethylene glycol monomethyl ether, (c) diethylene
glycol dimethyl ether; (D = (C2H4O)n H+, E = CH3
(OC2H4)n+ , F = CH3O (C2H4O)n+)
laboratory and those of the literature (although there is
no obvious pattern to the differences).
2334 Res. J. Appl. Sci. Eng. Technol., 5(7): 2332-2339, 2013
The spectra of the ethylene glycol monomethyl
ether, its ethyl and propyl analog (x = 1, 2, 3) do not
contain detectable molecular ions but show
distributions of ions similar to those of the analogous
hydrocarbons (CxH2x+1+, CxH2x-1+, CxH2x+, CxH2x-2+)
with additional oxygen containing ions derived from
the ethylene oxide units (CxH2x+1O+, CxH2xO+, CxH2x+
+
+
1O , C2H4OH , (HOC2H4OH) H ). However, the alkyl
fragment ions, oxygen containing fragment ions and
fragment ions separated by 44 mass units, will allow the
identification of these compounds as polyethylene
glycol derivatives. Alkyl ions with the same carbon
number as the alkyl groups attached to the ethylene
glycol unit are relatively abundant and therefore, allow
for a differentiation of each PEGMAE from each other
(x6).
The inductive cleavage reactions at the ether
oxygen of EGMAE can give four ionic products Eq. (1)
to (4), viz: Two α-cleavage product ions Eq. (5) to (7)
which produce alkyl ions. The C2H4OH+ ion (m/z 45)
becomes more abundant with increasing size of the
alkyl group. The ratio:
RO+.C2H4OH  R+ + .OC2H4OH
(1)
 +OC2H4OH + R
(2)
 C2H4OH+ + RO+
(3)
 RO+ + .C2H4OH
(4)
 RO+ = CH2 + .CH2OH
(5)
 CH2 = OH+ + ROCH2.
(6)
R+  lower alkyl fragment ions
(7)
of the I (R+) /I (RO+) ions Eq. (1), (7), increases with
increasing value of x for x = 1 - 6 and becomes very
small for x = 10 and 12 because of the subsequent
decomposition of the R+ ion to lower mass fragment
ions. These observations suggest: that the cleavage of
the R--O+ bond is favored over the cleavage of the RO-C bond.
The base peak in the spectrum of ethylene glycol
monomethyl ether is the ion at m/z 45, which is
probably both CH3O+ = CH2 (α-cleavage) and or
protonated ethylene oxide (inductive cleavage). The
base peak of ethylene glycol monoethyl ether is the ion
at m/z 31, which is probably formed from the terminal
CH2OH Eq. (6), cleavage of the C-O bond). As the size
of the alkyl group increases (x3), there are consecutive
decompositions of the saturated hydrocarbon ions
which resulted into lower alkyl fragment ions. The
abundances of these alkyl fragments reaches a
maximum at C3 (m/z 43) or C4 (m/z 57). The base peak
of EGMAE is either m/z 43 or 57 except that of
ethylene glycol mono nonlethal (m/z 69 (CxH2x-1+). The
lower mass CxH2x+1+ and CxH2x-1+ ions are also major
ions in the mass spectra of decanol and dodecanol (the
base peak at m/z 43). However, the CxH2x-1+ and CxH2x+
ions are more prominent in the mass spectra of decanol
and dodecanol than in those of EGMAE (Stein, 1997).
The ions in the series CxH2x+1+ are isobaric with the
ions in CxH2x-1O+ series. The CxH2x+1+ ion are formed by
charge-site cleavages of the ether C-O bond followed
by σ-cleavages of the C-C bonds. The CxH2x-1O+ ions
are also formed by charge-site cleavage of the ether CO bond followed by decompositions into lower mass
oxygen containing fragment ions or becomes
dehydrated to form CxH2x-1+ ions. In the EI mass spectra
of alcohols, McLafferty and Turecek (1993) showed
that ions such as C2H5+, CHO+ and C3H7+, C2H3O+
contributes to the relative abundance of ions at mass
m/z 29 and 43, respectively. The relative abundance of
m/z 29 (% total ionization) in this experiment decreases
with increasing x. This observation suggests that most
of m/z 29 ions are CHO+ ions and with some
contributions from C2H5+.
There is a series of nominal α-cleavage ions,
CxH2x+1O = CH2+, (31, 45, 59, 73, 87 and 101 m/z,
respectively) which are probably carbocations. These
carbocations may undergo hydrogen rearrangement to
the carbon atom of the oxonium double bond. The
rearrangement also involves loss of CxH2x ions to form
more CH3O+ or higher mass oxonium ions. The relative
abundances of these ions depend on the relative
abundance of its primary ions (Levin and Lias, 1971).
The ion at m/z 31 is the most abundant in this series and
its relative abundance (% Total Ionization, TIC)
decreases with increasing size of the alkyl group. This
observation suggests that the ions at m/z 31 are formed
mostly from the terminal HOCH2 with minimal
contribution from CH3O+ (Stephanou and Giger, 1982).
Ions at m/z 63, HOC2H4OH2+, only occur when
x3 and are likely to be formed by double hydrogen
rearrangement reactions. Its relative abundance (%
TIC) increases with increasing x and reaches a limiting
value of ~3.3% with ethylene glycol dodecyl ether.
There is another series of ions with nominal
composition of CxH2x-1+ (41, 55 and 69 m/z,
respectively) formed from the decomposition of the
alkyl fragment ion (CxH2x+1+.) or from the dehydration
of the CxH2x-1O+ ions. The relative abundances of these
ions (% TIC) increase with increasing value of x and
2335 Res. J. Appl. Sci. Eng. Technol., 5(7): 2332-2339, 2013
63
Ethylene glycol monobuty ether
45
57
MW = 118
180
19
0
200
210
220
61
43
119
73
75 8791
83 101
40
50
60
70
80
90
10
0
110
120
130
14
0
150
16
0
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Series of ions formed by the loss of neutral (H2O +
CxH2x) molecules (m/z 30, 44, 58...) were also
observed. These ions are formed in decreasing amounts
with increasing value of x for each of the monoalkyl
ethers and constitute ~2-7% of the total sample
ionization. A series of olefinic ions, CxH2x+ (m/z 42, 56,
70…) were also present in the spectra of these
monoalkyl ethers. The relative abundances of these ions
vary between ~3-8% of the total ionization.
The major ions in the EI mass spectra of
polyethylene glycol monodactyl and dodecyl ethers,
CxH2x+1 (OC2H4)n OH (x = 10,12; n = 1- 3), consist
mostly of low mass hydrocarbon homolog’s (~56-65%,
CxH2x+1+, CxH2x+, CxH2x-1+, CxH2x-2+, etc.) with
additional oxygen containing ions derived from
ethylene oxide units (~26-28%, CxH2x-1O+, CxH2xO+,
(C2H4O)n H+, HO (C2H4O)n H2+) and no molecular ions.
The base peaks in the spectra of these compounds are
variable and are determined by the hydrocarbon part of
the oligomer when n≤2, x≥3 and by the ethylene oxide
moiety when n≥3. The dominant cleavages in all
spectra of the monodactyl ethers are a chimerically
assisted charge-site cleavages and σ-cleavages. The
simple α-cleavage ions accompanied by hydrogen
rearrangement (31, 75, 119 and 163 m/z, respectively)
are not as prominent as those in the spectrum of PEG’s,
1-decanol and other alcohols (Onigbinde et al., 2001).
m/z
Ethylene glycol monodecyl ether.
57
MW = 202
71
85
147
97
91
141
m/z
203
171
16
0
17
0
180
19
0
200
210
220
131
111119
14
0
59
43
45
83
40
50
60
70
80
90
10
0
110
120
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
63
(a)
(b)
Fig. 3: CH4/CI mass spectra of (a) ethylene glycol monobutyl
ether (b) ethylene glycol monodactyl ether
m/z 69 is the base peak in the spectrum of ethylene
glycol monononyl ether. The sum of the relative
abundances of these ions varies from ~10% of the total
ionization for ethylene glycol monomethyl ether to
~30% in ethylene glycol dodecyl ether and are more
abundant in the mass spectra of decanol and dodecanol
than in the spectra of the corresponding ethylene glycol
monodactyl and dodecyl ethers (Stein, 1997).
Another decomposition pathway observed with the
lower mass ethylene glycol monoalkyl ethers (x = 1 - 4)
is the elimination of water (1-5% of total ionization).
The spectra of the higher EGMAE (x6) do not contain
(M-H2O)+ ions in contrast to the mass spectra of ndecanol and n-dodecanol (Harrison et al., 1971).
Chemical Ionization (CI): The methane CI (CH4) of
ethylene glycol monohexyl and monodactyl ether is
shown in Fig. 3. The methane CI mass spectra of these
compounds contain MH+ ions and fragment ions similar
to those found in their EI mass spectra. The relative
abundances of the MH+ ions are low, variable and
increase with increasing sample size across the
chromatographic peaks; hence, a major portion of these
ions are formed by sample ion/sample molecular
reactions. The relative abundances of the MH+ ions do
not increase with increasing x or n. The base peaks in
the spectra of these compounds under methane CI are
also variable and are determined by the ethylene oxide
moiety. For the low mass oligomers (x3), the base
peak are PEG related (e.g., m/z 45, 59) but those of
higher mass oligomers (x4) are MH+ ions (n3) and
sometimes ions formed by hydrogen rearrangement
decompositions of the MH+ ions (m/z 63 and 107, (HO
(C2H4O)2 H) H+ ( n = 1 - 2)). There are no (MH-H2O)+
ion or protonated dimer Ions (n2, x2) in the spectra
of PEGMAE. The relative abundances of the major
Ions decrease in the order of m/z 89>45>133>177 and
are different from the order in methane CI of PEG
oligomers (Onigbinde et al., 2001).
2336 Res. J. Appl. Sci. Eng. Technol., 5(7): 2332-2339, 2013
Relative molar sensitivity (RMS)
Table 1: Relative molar sensitivities of polyethylene glycol monoalkyl Ethers (EI)
c
d
e
f
α
P
RMS
RSG
Compound
GC
MW
MW ratio
Methoxy ethanol
a
76.1
0.31
7.42
0.26
0.28 (0.03)
0.91 (0.10)
b
0.30 (0.04)
0.97 (0.13)
Ethoxy ethanol
a
90.1
0.37
9.24
0.33
0.36 (0.05)
0.98 (0.14)
b
0.38 (0.04)
1.03 (0.11)
2-butoxy ethanol
a
118.1
0.48
12.90
0.46
0.48 (0.04)
1.00 (0.08)
b
0.46 (0.03)
0.96 (0.06)
Diethylene glycol mono methyl ether a
120.2
0.49
11.69
0.42
0.43 (0.07)
0.88 (0.14)
b
0.45 (0.03)
0.92 (0.06)
Diethylene glycol mono ethyl ether
a
134.2
0.55
13.51
0.48
0.51 (0.05)
0.94 (0.09)
b
0.51 (0.03)
0.94 (0.06)
Ethylene glycol mono hexyl ether
b
146.2
0.59
16.56
0.58
0.58 (0.03)
0.91 (0.05)
Diethylene glycol mono butyl ether
a
162.1
0.66
17.16
0.61
0.58 (0.01)
0.88 (0.02)
b
0.55 (0.04)
0.84 (0.06)
Diethylene glycol mono pentyl ether
a
176.1
0.72
18.97
0.68
0.63 (0.05)
0.88 (0.07)
b
0.75 (0.09)
1.05 (0.13)
Diethylene glycol mono hexyl ether
a
190.2
0.77
20.79
0.74
0.71 (0.05)
0.92 (0.06)
Ethylene glycol mono decyl ether
a
202.2
0.82
23.95
0.85
0.73 (0.06)
0.89 (0.07)
b
0.69 (0.02)
0.84 (0.02)
Ethylene glycol dodecyl ether
a
230.2
0.94
27.63
0.99
0.82 (0.01)
0.88 (0.01)
b
0.84 (0.04)
0.90 (0.04)
Diethylene glycol mono decyl ether
a
246.2
1.00
28.19
1.00
1.00
1.00
b
1.00
1.00
Diethylene glycol dodecyl ether
a
274.2
1.11
31.87
1.13
1.08 (0.07)
0.96 (0.06)
b
1.12 (0.04)
1.01 (0.04)
Triethylene glycol mono decyl ether
a
290.2
1.18
32.40
1.11
1.04 (0.05)
0.97 (0.05)
b
1.17 (0.03)
1.14 (0.03)
Triethylene glycol dodecyl ether
a
318.2
1.29
36.11
1.28
1.27 (0.08)
0.98 (0.06)
b
1.28 (0.05)
0.99 (0.04)
Tetraethylene glycol dodecyl ether
a
362.2
1.47
40.36
1.44
1.31 (0.06)
0.89 (0.04)
b
1.36 (0.04)
0.92 (0.03)
a
: HP5970; b: VG auto specQ, c: Molecular polarizability, calculated according to reference 20; d: Molecular polarizability ratio; e: RMS = Relative
molar sensitivity (calculated relative to diethylene glycol monodactyl ether = 1.00); f: RSG = Relative sensitivity per gram; Average of at least 5
GC/MS experiments Standard deviations given in parentheses
previously for the polyethylene glycols, hydrocarbons
and some PEGMAE (Harrison et al., 1971; Allgood
et al., 1990). Figure 4 shows a plot of relative molar
sensitivity, RMS, vs. polarizability ratio over the range
obtained with HP 5970 (MSD). A line of unit slope,
RMS = P, gives a reasonable fit (±10%) to the data. A
better fit to these data is achieved, however, with a nonzero intercept and a slope which is less than one:
LIT
PEG
PEGMAE
Unit slope
2
1
0
RMS = 0.96397P + 0.02387
0
1
Polarizability ratio
2
Fig. 4: Relative Molar Sensitivity (RMS) vs. polari ability
ratio
Relative molar sensitivities of polyethylene glycol
monoalkyl ethers: The Relative Molar Sensitivities
(RMS) for some PEGMAE obtained with a quadrupole
(MSD) and magnetic sector (VG Auto SpecQ) mass
spectrometers are given in Table 1. The agreement
between the two sets of data is satisfactory (±10%).
RMS of the PEGMAE increase with increasing
molecular weight or polarizability as observed
The data for the relative molar sensitivities of
polyethylene glycols reported by Onigbinde et al.
(2001) is also shown in Fig. 4. The data for the PEG
oligomers and the PEGMAE oligomers show
essentially the same variation with polarizability ratio.
The relative molar sensitivities of some PEGMAE (C10
- C12) obtained previously in this laboratory (Allgood
et al., 1990) were recalculated to C10 H21 (OC2H4)2 OH
and are also shown in Fig. 4. These data have a slope
significantly greater than one and do not overlap the
data obtained here. There is no obvious explanation for
these differences.
2337 Res. J. Appl. Sci. Eng. Technol., 5(7): 2332-2339, 2013
Table 1 also lists the Relative Sensitivity per Gram
(RSG) for the PEGMAE. To a reasonable
approximation, one can consider the RSG to be unity;
therefore, area percent from a chromatographic trace
would be the same as the weight percent. The average
value for the relative sensitivities per gram is 0.92
(±0.05).
CONCLUSION
The EI mass spectra of low mass PEGMAE, like
those of similar hydrocarbons, alcohols and ethers,
show low abundance of molecular ions (x3, n = 1 - 4).
The higher members of this series (x4, for all n) do not
contain molecular ions in their EI mass spectra. The
major ions in the EI spectra of all PEGMAE are:
CxH2x±1+, CxH2x+, CxH2x-2+, CxH2x-1O+, CxH2xO+,
(C2H4O)n H+, HO (C2H4O)n H2+. There are no (M-H2O)+
ions in the mass spectra of PEGMAE for n2 and the
relative abundances of the characteristic CxH2x+1+ ions
decrease with increasing x. The base peaks in the CI
spectra of these compounds are variable and are
determined by the hydrocarbon part of the oligomers
when n2, x3 and by the ethylene oxide moiety when
n3. The dominant cleavages in all spectra of
PEGMAE are a chimerically assisted charge-site
cleavages and alpha cleavages. The relative molar
sensitivities, RMS, for these compounds increase
linearly with increasing molecular polarizability or
molecular weight. THE RMS under EI conditions
shows a non-zero intercept and a slope less than one
which is different from the one previously reported with
a slope greater than 1.
ACKNOWLEDGMENT
All work was done in the laboratory of Professor
Burnaby Munson at the University of Delaware.
Newark, Delaware. USA.
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